.filter 
  position: relative
  z-index: 3
  height: 40px
  .mask 
    position: fixed
    z-index: 2
    left: 0
    right: 0
    top: 0
    bottom: 0
    background-color: rgba(0, 0, 0, 0.5)
    opacity: 1
  .filter-box 
    position: absolute
    z-index: 3
    width: 100%
    background-color: #fff
